[unreadable] Nitric oxide (NO) plays a fundamental role in maintaining normal vasomotor tone. Its bioavailability is dependent on its production from endothelial nitric oxide synthase and its consumption by hemoglobin. Disruption in NO homeostasis may lead to dysregulation of vasomotor tone. Acute intravascular hemolysis is characterized by the release of hemoglobin from the erythrocyte into the plasma (cell-free plasma hemoglobin). Our group has shown that cell-free plasma hemoglobin scavenges endogenous nitric oxide 600-fold faster than intra-erythrocytic hemoglobin and therefore may acutely disrupt NO homeostasis. We hypothesize that disruption in nitric oxide homeostasis during hemolysis may cause endothelial dysfunction and produce vasoconstriction, hypoperfusion, and subsequent end organ injury. Furthermore, therapy with nitric oxide donor agents may attenuate the physiologic derangements that lead to organ injury during acute hemolytic episodes. In order to study this we will (1) examine the effects of various levels of cell-free plasma hemoglobin on systemic and pulmonary hemodynamics, end-organ function, and endothelial cell function in a canine model of intravascular hemolysis; (2) quantitate the ability of both inhaled nitric oxide and intravenous sodium nitrite to selectively oxidize cell-free plasma hemoglobin and attenuate the physiologic changes induced in the canine hemolysis model;(3) examine the role of cell-free plasma hemoglobin in the pathophysiologic changes and end-organ injury that occurs in prolonged cardiopulmonary bypass (CPB), an acute, iatrogenic hemolytic state that is common, predictable, and accessible for study in humans. This project will characterize a mechanism for physiologic changes and end-organ injury which may be involved in many human hemolytic diseases. Furthermore, it will investigate the therapeutic role of nitric oxide donor agents to attenuate hemolysis-induced physiologic changes. The results of our studies will be of critical importance to understanding the complications that occur in human hemolytic diseases and in the development of therapy for these diseases. Studying nitric oxide biochemistry and its interactions with hemoglobin in the laboratories of Drs. Gladwin and Schechter in the NIDDK will allow me to acquire the knowledge base and research tools to become an independent investigator [unreadable] [unreadable]